1. FIELD OF THE INVENTION
The present invention relates to a device for monitoring abrasion loss of a thrust bearing in a submerged motor pump.
2. DESCRIPTION OF THE RELATED ART
A plant which handles a fluid of a special kind or a fluid at high temperature and high pressure, such as a thermal electric power plant, a nuclear power plant, an oil (refining) plant or a chemical plant, normally employs an enclosed submerged motor pump comprising a pump and motor, such as a canned motor or a wet stator motor, which are formed together without a shaft seal between the pump and the motor.
If a detector is provided inside the motor for examining the motor, the construction of the submerged motor pump becomes complicated. Moreover, if a part of the detector should come off or break up, the separated part or portion will very likely hit and damage a bearing, a stator or a rotor of the motor and cause trouble.
Therefore, an ammeter, a thermometer and a vibrometer for examining the motor indirectly are mounted on the outside of the motor casing in a known submerged motor pump.
However, since the motor is indirectly examined by observing the values indicated by the ammeter, the thermometer and the vibrometer or the transition of the indicated values, it is extremely difficult to precisely quantitate abrasion loss of a thrust bearing in an early stage. The abrasion loss of the thrust bearing is one of the important factors to be monitored in a submerged motor pump.
In the submerged motor pump, a pump shaft connected to a pump impeller is radially supported by a journal bearing and axially supported by the thrust bearing. Abrasion loss of the journal bearing is comparatively easy to detect because such abrasion loss is likely to cause a change in the vibration. On the other hand, abrasion loss of the thrust bearing is difficult to detect because it hardly causes any significant change in the values indicated by the ammeter, the thermometer and the vibrometer or the transition of these values. Therefore, it is not detected before the abrasion loss of the thrust bearing has reached an abnormal level. Abrasion loss of the thrust bearing can be accurately measured only when the submerged motor pump is disassembled.
In practice, therefore, a submerged motor pump is periodically disassembled to check out abrasion loss of the thrust bearing and replace worn parts if necessary. The interval between such periodical inspection is determined based on experience.
However, the rate of abrasion of the thrust bearing greatly varies depending on operating hours, times of starting and stopping, and contaminants (solid materials) in the fluid. In some cases, abrasion of the thrust bearing progresses much faster than expected.